Stress within vocal fold tissue is a primary source of vocal fold discomfort and damage. Identifying the influence of various factors that contribute to vocal fold stress can lead to improved clinical care, improved medical procedures, and increased awareness of individuals in the workforce who rely on voice use. One source of vocal fold stress is that which results from increased adhesive properties of the glottal airway surface liquid (ASL). Such situations can arise, for example, from dehydration. The goal of the proposed research is to develop models for studying the glottal ASL and use these models to explore the sensitivity of vocal fold stress and function to ASL adhesion forces. Pursuit of this goal is planned through the use of complementary analytical, synthetic, and computational vocal fold models according to the following research aims: Specific Aim 1: Develop airway surface liquid models for use in computational vocal fold models. Develop analytical and computational (finite element) models of glottal airway surface liquid (ASL). Incorporate two- layer ASL representation, namely, Newtonian sol layer and non-Newtonian mucus layer. Validate models with experiments carried out using mono- and bi-layer Newtonian and non-Newtonian fluids, including sol and mucus simulants. Specific Aim 2: Incorporate airway surface liquid models in self-oscillating computational vocal fold models. Incorporate ASL models into self-oscillating models of vocal fold vibration, including a two-dimensional, body- cover finite element (FE) vocal fold model and a three-dimensional, multi-tissue-layer FE vocal fold model. Validate models with data from experiments using synthetic self-oscillating vocal fold models. Specific Aim 3: Investigate sensitivity of vocal fold stress and function during phonation to airway surface liquid properties using computational vocal fold models. Using the FE vocal fold + ASL models (Specific Aim 2), identify conditions in which ASL adhesion forces become sufficiently large so as to significantly influence vocal fold stress and function. Perform parametric sensitivity studies using different values of ASL thickness and properties, vocal fold tissue layer geometry and properties, and oscillation parameters. Observables include stress within the vocal fold cover, oscillation frequency and amplitude, open quotient, glottal airflow waveforms, and frequency vs. pressure and flow rate vs. pressure relationships. Accomplishing the above aims will impact several areas of voice care and research, including: engineered tissue development for replacing damaged vocal fold tissue, vocal fold prosthesis and implant design, voice disorder treatment, and voice production research. Project Narrative: The airway surface liquid (ASL) lines the human respiratory airways. Under certain conditions the glottal ASL is subject to dehydration and other property changes that may adversely influence voice production. The objective of the proposed research is to develop models of the glottal ASL and explore its influence on vocal fold tissue stress and vibratory behavior.